Generally, acrylonitrile-butadiene-styrene (ABS) resin is used in various applications, comprising vehicle parts, electric home appliances, and office automation (OA) devices such as printers or scanners, because it has a good balance of processability of styrene, toughness and chemical resistance of acrylonitrile and impact resistance of butadiene, and has an excellent appearance.
However, ABS resin has a shortcoming in that it is opaque, and thus use thereof in parts requiring transparency, such as a transparent window for a microwave oven, a cleaner duct, a housing for a TV, a housing for a game console, and a transparent window for office equipment is limited. Due to this shortcoming, transparent materials have recently been actively developed.
Transparent resins that are used mainly in products requiring transparency comprise styrene-acrylonitrile resin, polycarbonate, general purpose polystyrene (GPPS), polymethylmethacrylate and transparent ABS resin. Among these resins, thermoplastic transparent resins such as transparent ABS have high impact strength and processability compared to other resins, and thus have recently been actively studied.
However, transparent ABS resin has poor weather resistance due to the characteristics of butadiene rubber used as an impact modifier in the transparent ABS resin, and thus use thereof has been limited.
In addition, transparent resins containing butadiene rubber also have limited transparency. Specifically, when the rubber content of these transparent resins is as low as 5% or less, the resins have excellent transparency, but when the rubber content of the resins is more than 5%, the resins have poor transparency, and thus have a haze value higher than that of polycarbonate (PC) or polymethylmethacrylate (PMMA).
Furthermore, these resins have a poor color, and for this reason, the color thereof is adjusted using a colorant during an extrusion or injection molding process. Nevertheless, these resins do not have a color close to natural color, and thus use thereof is limited.
Meanwhile, to achieve a high degree of conversion at low reaction temperature, a redox system is mainly used during polymerization. To form the redox system, the following three methods are typically used: a method of adding a colloidal dispersion of Fe2+; a method of adding reducing sugar (fructose, etc.); and a method of using sodium formaldehyde sulfoxylate (SFS).
Among these methods, sodium formaldehyde sulfoxylate (SFS) is mainly used, because it enables reduction in the amount of iron (Fe) ions compared to other systems.
For reference, if Fe ions remain in a product, they will discolor the product and reduce the thermal stability of the product. If Fe ions are not used during polymerization for this reason, the degree of conversion will be significantly reduced, and thus the yield of the product will be reduced and the content of residual monomers in the product will also increase, adversely affecting the physical properties of the product.
Meanwhile, if sodium formaldehyde sulfoxylate (SFS) is used, there will be a shortcoming in that, because sodium formaldehyde sulfoxylate (SFS) is sodium sulfinate and formaldehyde, environmentally harmful formaldehyde will be emitted during post-treatment of the product.
Accordingly, there is a need for a technology which enables a resin product to have a good color close to natural color and to ensure weather resistance, without having to use sodium formaldehyde sulfoxylate (SFS) and Fe ions.